Histoplasma capsulatum. Methenamine silver stain showing histopathologic changes in histoplasmosis. (Source: Centers for Disease Control and Prevention Public Health Image Library)
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Histoplasmosis

Histoplasmosis is a disease caused by the fungus Histoplasma capsulatum. Its symptoms vary greatly, but the disease primarily affects the lungs. Occasionally, other organs are affected—this form of the disease is called disseminated histoplasmosis, and it can be fatal if untreated. more...

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H. capsulatum is found throughout the world and is endemic in certain areas of the United States. The fungus has been found in poultry house litter, caves, areas harboring bats, and in bird roosts(especially Starlings).

Incidence

Positive histoplasmin skin tests occur in as many as 80% of the people living in areas where H. capsulatum is common, such as the eastern and central United States. Infants, young children, and older persons, in particular those with chronic lung disease, are at increased risk for severe disease. Disseminated disease is more frequently seen in people with cancer or AIDS.

Causes

H. capsulatum grows in soil and material contaminated with bat or bird droppings. Spores become airborne when contaminated soil is disturbed. Breathing the spores causes infection. The disease is not transmitted from an infected person to someone else.

Transmission

H. capsulatum grows in soil and material contaminated with bat or bird droppings. Spores become airborne when contaminated soil is disturbed. Breathing the spores causes infection. The disease is not transmitted from an infected person to someone else.

Symptoms

If symptoms occur, they will start within 3 to 17 days after exposure; the average is 10 days. Most infected persons have no apparent ill effects. The acute respiratory disease is characterized by respiratory symptoms, a general ill feeling, fever, chest pains, and a dry or nonproductive cough. Distinct patterns may be seen on a chest x-ray. Chronic lung disease resembles tuberculosis and can worsen over months or years. The disseminated form is fatal unless treated.

Treatment

Antifungal medications are used to treat severe cases of acute histoplasmosis and all cases of chronic and disseminated disease. Mild disease usually resolves without treatment. Past infection results in partial protection against ill effects if reinfected.

Prevention

It is not practical to test or decontaminate most sites that may be contaminated with H. capsulatum, but the following precautions can be taken to reduce a person's risk of exposure:

  • Avoid areas that may harbor the fungus, e.g., accumulations of bird or bat droppings.
  • Before starting a job or activity having a risk for exposure to H. capsulatum, consult the NIOSH/NCID Document Histoplasmosis: Protecting Workers at Risk. This document contains information on work practices and personal protective equipment that will reduce the risk of infection.

Note: The original version of this article is adapted from the U.S. CDC public domain document at

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Histoplasmosis
From Gale Encyclopedia of Medicine, 4/6/01 by Tish Davidson

Definition

Histoplasmosis is an infectious disease caused by inhaling the microscopic spores of the fungus Histoplasma capsulatum. The disease exists in three forms. Acute or primary histoplasmosis causes flu-like symptoms. Most people who are infected recover without medical intervention. Chronic histoplasmosis affects the lungs and can be fatal. Disseminated histoplasmosis affects many organ systems in the body and is often fatal, especially to people with acquired immunodeficiency syndrome (AIDS).

Description

Histoplasmosis is an airborne infection. The spores that cause this disease are found in soil that has been contaminated with bird or bat droppings. In the United States, the disease is most common in eastern and midwestern states and is widespread in the upper Mississippi, Ohio, Missouri, and St. Lawrence river valleys. Sometimes histoplasmosis is called Ohio Valley disease, Central Mississippi River Valley disease, Appalachian Mountain disease, Darling's disease, or Histoplasma capsulatum infection.

Anyone can get histoplasmosis, but people who are come into contact with bird and bat excrement are more likely to be infected. This includes farmers, gardeners, bridge inspectors and painters, roofers, chimney cleaners, demolition and construction workers, people installing or servicing heating and air conditioning units, people restoring old or abandoned buildings, and people who explore caves.

The very young and the elderly, especially if they have a pre-existing lung disease or are heavy smokers, are more likely to develop symptoms that are more severe. People who have a weakened immune system, either from diseases such as AIDS or leukemia, or as the result of medications they take (corticosteroids, chemotherapy drugs), are more likely to develop chronic or disseminated histoplasmosis.

Causes & symptoms

When the spores of H. capsulatum are inhaled, they lodge in the lungs where they divide and cause lesions. This is known as acute or primary histoplasmosis. It is not contagious.

Many otherwise healthy people show no symptoms of infection at all. When symptoms do occur, they appear 3-17 days after exposure (average time is 10 days). The symptoms are usually mild and resemble those of a cold or flu; fever, dry cough, enlarged lymph glands, tiredness, and a general feeling of ill health. A small number of people develop bronchopneumonia. About 95% of people who are infected either experience no symptoms or have symptoms that clear up spontaneously. These people then have partial immunity to re-infection.

In some people, the spores that cause the disease continue to live in the lungs. In about 5% of people who are infected, usually those with chronic lung disease, diabetes mellitis, or weakened immune systems, the disease progresses to chronic histoplasmosis. This can take months or years. Symptoms of chronic histoplasmosis resemble those of tuberculosis. Cavities form in the lung tissue, parts of the lung may collapse, and the lungs fill with fluid. Chronic histoplasmosis is a serious disease that can result in death.

The rarest form of histoplasmosis is disseminated histoplasmosis. Disseminated histoplasmosis is seen almost exclusively in patients with AIDS or other immune defects. In disseminated histoplasmosis the infection may move to the spleen, liver, bone marrow, or adrenal glands. Symptoms include a worsening of those found in chronic histoplasmosis, as well as weight loss, diarrhea, the development of open sores in the mouth and nose, and enlargement of the spleen, liver, and adrenal gland.

Diagnosis

A simple skin test similar to that given for tuberculosis will tell if a person has previously been infected by the fungus H. capsulatum. Chest x rays often show lung damage caused by the fungus, but do not lead to a definitive diagnosis because the damage caused by other diseases has a similar appearance on the x ray. Diagnosis of chronic or disseminated histoplasmosis can be made by culturing a sample of sputum or other body fluids in the laboratory to isolate the fungus. The urine, blood serum, washings from the lungs, or cerebrospinal fluid can all be tested for the presence of an antigen produced in response to the infection. Most cases of primary histoplasmosis go undiagnosed.

Treatment

Acute primary histoplasmosis generally requires no treatment other than rest. Non-prescription drugs such as acetaminophen (Tylenol) may be used to treat pain and relieve fever. Avoiding smoke and using a cool air humidifier may ease chest pain.

Patients with an intact immune system who develop chronic histoplasmosis are treated with the drug ketoconazole (Nizoral) or amphotericin B (Fungizone). Patients with suppressed immune systems are treated with amphotericin B, which is given intravenously. Because of its potentially toxic side effects, hospitalization is often required. The patient may also receive other drugs to minimize the side effects of the amphotericin B.

Patients with AIDS must continue to take the drug itraconazole (Sporonox) orally for the rest of their lives in order to prevent a relapse. If the patient can not tolerate itraconazole, the drug fluconazole (Diflucan) can be substituted.

Alternative treatment

In non-immunocompromised patients, alternative therapies can be very successful. Alternative treatment for fungal infections focuses on creating an environment where the fungus cannot survive. This is accomplished by maintaining good health and eating a diet low in dairy products, sugars, including honey and fruit juice, and foods like beer that contain yeast. This is complemented by a diet high in raw food. Supplements of antioxidant vitamins C, E, and A, along with B complex, may also be added to the diet. Lactobacillus acidophilus and Bifidobacteria will replenish the good bacteria in the intestines. Antifungal herbs, like garlic, can be consumed in relatively large does and for an extended period of time in order to be most effective.

Prognosis

Most people recover from primary histoplasmosis in a few weeks without medical intervention. Patients with chronic histoplasmosis who are treated with antifungal drugs generally recover rapidly if they do not have an underlying serious disease. When left untreated, or if serious disease is present, histoplasmosis can be fatal.

AIDS patients with disseminated histoplasmosis vary in their response to amphotericin B, depending on their general health and how well they tolerate the side effects of the drug. Treatment often suppresses the infection temporarily, but patients with AIDS are always in danger of a relapse and must continue to take medication for the rest of their lives to keep the infection at bay. New combinations of therapies and new drugs are constantly being evaluated, making hard statistics on prognosis difficult to come by. AIDS patients have problems with multiple opportunistic infections, making it difficult to isolate death rates due to any one particular fungal infection.

Prevention

Since the spores of H. capsulatum are so widespread, it is almost impossible to prevent exposure in endemic areas. Dust suppression measures when working with contaminated soil may help limit exposure. Individuals who are at risk of developing the more severe forms of the disease should avoid situations where they will be exposed to bat and bird droppings.

Key Terms

Acidophilus
The bacteria usually found in yogurt.
Adrenal gland
A pair of organs located above the kidneys. The outer tissue of the gland produces the hormones epinephrine (adrenaline) and norepinephrine, while the inner tissue produces several steroid hormones.
Antigen
A foreign protein to which the body reacts by making antibodies.
Bifidobacteria
A group of bacteria normally present in the intestine. Commercial supplements are available.
Corticosteroids
A group of hormones produced naturally by the adrenal gland or manufactured synthetically. They are often used to treat inflammation. Examples include cortisone and prednisone.

Further Reading

For Your Information

    Books

  • Griffith, H. Winter. Complete Guide to Symptoms, Illness & Surgery. Putnam Berkely Group, 1995.

    Periodicals

  • Centers for Disease Control and Prevention. Histoplasmosis: Protecting Workers at Risk. (September 1997). http://www.cdc.gov/niosh/97146eng.html.
  • Medical Mycology Research Center. Histoplasmosis capsulati and Histoplasmosis duboisii. University of Texas Medical Branch at Galveston. (May 1997). http://www.fungus.utmb.edu.

    Organizations

  • American Lung Association. 800-LUNG-USA. http://www.lungusa.org.
  • National Center for Infectious Diseases. Atlanta, Georgia. 404-639-3158. www.cdc.gov/ncidod/ncid/ncid.htm.
  • National Institute for Occupational Safety and Health. Cincinnati, Ohio. 800-356-4674.

Gale Encyclopedia of Medicine. Gale Research, 1999.

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